Previously known specimen prealigners and robot arm mechanisms employ separate units to perform their specimen handling and prealignment functions serially. Such separate and serial operation naturally leads to reduced specimen handling throughput and precision, creates added expense, and requires an increased work area. These considerations have increasing importance as specimens grow in size, such as semiconductor wafers that are now twelve inches in diameter.
U.S. Pat. No. 5,102,280 of Poduje et al. for ROBOT PREALIGNER describes a robot arm adapted to fetch a substantially disk-shaped specimen from a holder at a first location and elevation and to transport the specimen in a combination of angular, radial, and elevational (Z-axis) movements to a separate prealigner. The prealigner includes a rotating support at a second fixed location and elevation and an edge detector that cooperate to sense offset and angle data as the specimen rotates on the support. The prealigner rotates the specimen to a predetermined angular alignment and, the robot arm fetches the specimen at an offset compensated orientation from the support and transports it to a processing station at yet another location and elevation. Such a specimen transporting and prealignment process involves considerable wasted motion.
U.S. Pat. No. 5,513,948 of Bacchi et al. for UNIVERSAL SPECIMEN PREALIGNER, which is assigned to the assignee of this application, describes an improved specimen prealigner in which the rotating platform is further controllably movable in X-axis and Y-axis directions. The prealigner also includes a linear optical array edge detector that cooperates with the X-axis, Y-axis, and rotating movements of the prealigner to rapidly sense offset and angular data for a wide variety of irregularly shaped specimens, such as semiconductor wafers, computer hard disks, or compact disks. Such a prealigner is particularly well-suited to edge sensing semiconductor wafers having alignment flats and notches and some degree of eccentricity. However, the cooperation between the robot arm and the prealigner still requires considerable wasted motion.
The previously known robot arm mechanisms typically employed with prealigners each include pivotally joined multiple links that are driven by a first motor and are mechanically coupled to effect straight line movement of an end effector or hand and are equipped with a second, independently operating motor to angularly displace the hand about a central axis. Certain robot arm mechanisms are equipped with telescoping mechanisms that move the hand in a direction perpendicular to the plane of straight line movement and angular displacement of the hand. The hand is often provided with a vacuum outlet that secures the specimen to the hand as it transports the specimen between processing stations.
U.S. Pat. No. 4,897,015 of Abbe et al. for ROTARY TO LINEAR MOTION ROBOT ARM describes a rotary-to-linear motion robot arm that uses a first motor to control a multi-linkage robot arm to produce straight line radial motion from motor-driven rotary motion. An additional motor may be coupled to the robot arm for operation independent of that of the first motor to angularly move the multi-linkage robot arm without radial motion. Because they independently produce radial motion and angular motion, the first and second motors produce useful robot arm movement when either is operating.
The robot arm of the Abbe et al. patent extends and retracts an end effector, or a hand, along a straight line path by means of a mechanism that pivotally couples in a fixed relationship a first arm, or forearm, and a second arm, or upper arm, so that they move in predetermined directions in response to rotation of the upper arm. To achieve angular displacement of the hand, a .theta. drive motor rotates the entire robot arm structure. The Abbe et al. patent describes no capability of the robot arm to travel along any path other than a straight line or a circular segment defined by a fixed radius.
U.S. Pat. No. 5,007,784 of Genov et al. for DUAL END EFFECTOR ROBOTIC ARM describes a robot arm with an end effector structure that has two oppositely extending hands, each of which is capable of picking up and transporting a specimen. The end effector structure has a central portion that is centrally pivotally mounted about the distal end of a second link or forearm. The extent of pivotal movement about all pivot axes is purposefully limited to prevent damage to vacuum pressure flexible conduits resulting from kinking or twisting caused by over rotation in a single direction.
U.S. Pat. No. 5,064,340, also of Genov et al., for PRECISION ARM MECHANISM describes three link and four link robot arms with single-ended end effector structures that are capable of picking up and transporting a specimen. The four link robot arm has extended reach capability combined with a reduced work area requirement. The coupling mechanisms of the robot arm links of the Genov et al. patents is more complex than that of the robot arm of the Abbe et al. patent. Nevertheless, the robot arm structures of the Abbe et al. and Genov et al. patents operate similarly in that each of the end effector structures picks up and transports specimens by using one motor to extend and retract a hand and another, different motor to rotate the entire robot arm structure to allow the hand to extend and retract at a restricted number of different angular positions.
Robot arms of the type described by the Abbe et al. and Genov et al. patents secure a specimen to the hand by vacuum pressure delivered to the hand through vacuum conduits extending through the upper arm, forearm, and hand and around all of the pivot axes. The Abbe et al. patent is silent about a vacuum pressure delivery system, and the Genov et al. patent describes the use of flexible vacuum conduits. The presence of flexible vacuum conduits limits robot arm travel path planning because unidirectional robot arm link rotation about the pivot axes "winds up" the conduits and eventually causes them to break. Thus, preventing conduit breakage requires prohibiting continuous robot arm rotation about any of the pivot axes and necessitates rewind maneuvers and travel path "lockout" spaces as part of robot arm travel path planning. The consequences of such rewind maneuvers are more complex and limited travel path planning, reduced throughput resulting from rewind time, and reduced available work area because of the lockout spaces.
A further problem caused by separate robot arms and prealigners is loss of absolute specimen positioning accuracy when the specimen is transferred from the robot arm, to the prealigner, and back to the robot arm. The prealigner places the specimen in a predetermined alignment, but may alter the specimen positioning such that the robot arm requires a corrected reach angle and reach extension to place the specimen on its intended target location.
What is needed, therefore, is a specimen handling and prealigner system that is capable of handling large specimens with improved throughput, extended reach, high prealignment accuracy, reach angle and extension correction, reduced work area requirement, and no movement restrictions.